Acid pickling bath containing inhibitor and method of treating ferrous metals



United States Patent ACID PICKLING BATH CONTAINING INHIBITOR AND METHOD OF TREATING FERROUS METALS Thomas W. Findley, La Grange, and Burton H. Robin and John E. Farbak, Chicago, Ill., assignors to Swift &

Company, Chicago, 11]., a corporation of Illinois No Drawing. Filed Jan. 23, 1957, Ser. No. 635,585

13 Claims. (Cl. 252-148) The present invention relates to pickling methods and compositions and to corrosion and rust inhibiting materials and processes.

A dark coating of iron oxide (mill scale) forms on the surface of iron and steel during certain processing steps such as hot rolling and forging. This oxide film must be removed before the metal can be cold rolled, galvanized, tinned, electroplated, etc. In commercial operations mill scale is usually eliminated by pickling the iron or steel sheets, plates, bars, etc., in a suitable acid solution. In order to be acceptable, the acid pickling bath should be capable of casting oif or dissolving the scale without unduly attacking the surface of the metal itself.

Although pickling is effective in removing mill scale, the acid treatment highly activates the surface of the treated metal, which immediately rusts on contact with oxygen. This rusting occurs as a flash reaction after the metal is water rinsed to free it from acid and while it is being air dried. Immediate rusting of this type is referred to as sulling or flash rusting and constitutes a serious problem in any industry where a rust-free metal is required.

Inasmuch as commercial pickling operations are often carried out under extreme conditions, materials added to a pickling bath to control corrosion, rust, etc., must be capable of performing at high acid concentrations and high temperature levels. Ordinarily, steel, for example, is pickled in a bath containing from about 10 percent to 25 percent H 80 for about /2 minute to 5 minutes at a temperature of about 75 C. to about 106 C.

Another problem often encountered in pickling processes is the escape of acid fumes from the bath into the atmosphere. These fumes have long troubled steel producers. They constitute a hazard and are a source of discomfort to workers in the area of the pickling operations. In addition, the fumes tend to corrode nearby machinery and structures.

A continuing search has been carried out to find substances which, when added to acid pickling baths, acid scrubbers, and rinse baths, would lessen corrosion losses and would prevent sulling and the formation of harmful fumes. Although many additives have proved to be helpful for these purposes, none of the materials heretofore discovered have been entirely satisfactory.

It is, therefore, an object of the present invention to provide new pickling compositions and new pickling methods which protect metal surfaces against acid attack without diminishing the ability of the pickling bath to remove oxide film.

An additional object of the present invention is to provide pickling compositions and pickling methods which substantially eliminate flash rusting or sulling.

A further object is to provide improved pickling compositions and pickling methods capable of removing oxide film without causing the evolution of harmful amounts of fumes from the pickling bath.

Another object of the present invention is to provide an improved iron and steel rinsing composition and method of rinsing iron and steel which substantially prevents immediate rusting.

A further object of the present invention is to pro- 3,033,796 Patented May 8, 1962 ICC vide a method of pickling iron and steel which prolongs the life of the acid bath.

Other objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description.

Generally, the present invention comprises the discovery that conventional pickling, scrubbing, and rinse baths can be greatly improved by adding to said baths a member taken from the group having the following general formula:

where m is in integer from 0 to 19, n is an integer from 0 to 4, p is an integer from 0 to 19, y is an integer from 0 to 17 and m+2n+ny+3+p=an integer from 10 to 22; where at least one of W and X is selected from the group consisting of [-NR'R"H]+[An], and -NRR"; where W is selected from the group consisting of and --NRR" when X is selected from the group consisting of H and OH; and where W is selected from the group consisting of [--NRRH]+[An]-, NR'R", H and OH when X is selected from the group consisting of [-NRR"H]+[An]-, and -NRR"; and where R is selected from the group consisting of alkyl and alkylol, R" is selected from the group consisting of H, alkyl and alkylol, where Z is selected from the group consisting of CH OH, COOH, CONR'R" and COOC H NRH where s is an integer from 2 to 8 and where [An] is an anion.

Pickling solutions containing widely divergent amounts of the above described ingredients have been found to be elfective in inhibiting corrosion, controlling harmful fumes, substantially preventing flash rusting or sulling, etc. Solutions having an inhibitor concentration of only 0.001 percent, for example, will improve the pickling operation, whereas satisfactory results can be obtained when as much as 25 percent or more of the ingredient is added to the baths. The effectiveness of the inhibiting compound does not evidence a sharp break when the concentration is changed. Although the amount of inhibitor added to the bath can vary extensively, it has been found that a concentration range of between about 0.01 percent and about 5.0 percent is preferred in most cases. Sulfuric acid is normally selected as the pickling acid in commercial operations. Other acids such as hydrochloric, phosphoric, and sulfamic, however, are like- Wise suitable.

The inhibitors of the present invention can be prepared by reacting a fatty material such as an epoxy, halogenated or halohydroxylated fatty acid, ester, amide, or alcohol having an alkyl chain length of from 10 to 22 carbon atoms with a primary or secondary alkylamine or alkylolamine. Examples of compounds formed in the above reactions are: hydroxy alkylamino fatty acids and their esters and amides; hydroxy alkylolamino fatty acids and their esters and amides; alkylamino fatty acids and their esters and amides; and alkylolamino fatty acids and their esters and amides. The preparation of alkylolamino fatty acids and their esters and amides is described in United States Patent No. 2,277,016. Hydroxy alkylamino fatty acids can be made as indicated in United States Patent No. 2,445,892. Methods of preparing hydroxy alkylolamino fatty acids and their esters and amides and hydroxy alkylolamino fatty alcohols are shown in copending United States Patent application Serial No. 629,235, filed December 19, 1956, and now US. Patent No. 2,993,919, under the name of New Compositions of Matter."

The following examples show the use of the present invention in treating iron and steel products.

Example I A pickling bath comparable to that used in the steel industry to remove mill scale was prepared by heating a 20 percent sulfuric acid solution to 95 C. Another bath was prepared in the same manner except that one (1) percent by weight of 9,l(10,9)diethanolaminohydroxystearic acid diethanolamide formed by condensing chlorohydroxystearic acid and diethanolamine was dissolved in the solution. Steel coupons cut from a steel sheet covered with mill scale were degreased and Weighed and were then immersed in the pickling baths for 30 seconds, minutes, and 30 minutes. The coupons were then rinsed in a water bath, allowed to air dry, and were again weighed. The following results were obtained:

Control 30 secondsLoss in weight= 1% CHSADEA 30 seconds-Loss in weight:

Control 5 minutesLoss in weight:

1% CHSADEA 5 minutes-Loss in weight:

Control 30 minutes-Loss in weight:

407 gJm.

1% CHSADEA 3O minutes-Loss in weight:

Weight losses in the above chart and in the examples to follow are expressed in grams per square meter of coupon surface.

During the treatment, each of the control samples reacted vigorously with the acid, causing the evolution of considerable hydrogen gas. In contrast, coupons immersed in the baths containing the inhibitor reacted significantly less with the acid and very little hydrogen was given off. On being removed from the rinse bath and air dried, the control coupons rusted severely during drying, whereas the treated coupons remained shiny.

Example 11 Two pickling baths containing 20 percent H 80 were heated to 95 C. To one of the baths was added one (1) percent by weight of the reaction product of diethanolamine methyldichloro stearate, which is principally bis[N,N-bis (fi-hydroxyethyl) amino] stearic acid diethanolamide. Steel coupons were pickled in each of the baths for 30 seconds, 5 minutes, and 30 minutes. The results of the treatment were as follows:

Control 30 seconds--Loss in weight:

1% MDCSDEA 30 seconds-Loss in weight Control 5 minutes-Loss in weight:

1% MDCSDEA 5 minutes-Loss in weight:

Control 30 minutesLoss in weight:

1% MDCSDEA 30 minutes-Loss in weight:

The coupons treated in the bath containing the inhibitor were found to be rust-free after the rinsing step, whereas coupons from the control bath rusted immediately on air-drying. The evolution of acid fumes was substantially eliminated in the MDCSDEA bath.

Example III Steel coupons were pickled for various lengths of time in a pickling bath prepared as shown in Example I except that the inhibitor was the diethanolamine condensate of methylpentachlorostearate, which is principally pentakis 4 [N,N-bis (B-hydroxyethyl) amino] stearic acid diethanolamide. The weight losses of the coupons were as follows:

30 seconds33.9 g./m. 5 minutes-42.3 g./m. 30 minutes-44.3 g./m.

After the coupons were rinsed and air-dried, they were found to be rust-free. In addition, no acid fumes were observed to have evolved from the bath.

Example IV Coupons were pickled in a bath, prepared as shown in Example I, which contained one (1) percent by weight of the diethanolamine condensate of alpha-bromostearic acid, which is principally a-[N,N-blS (,B-hydroxyethyl) amino] stearic acid diethanolamide. The weight losses of the coupons were as follows:

30 seconds33.2 g./m. 5 minutes40.5 g./m. 30 minutes-46.1 g./m.

After the coupons were rinsed and air-dried, they were found to be rust-free. Again, no acid fumes were given off by the bath.

Example V One (1) percent by weight of the diethanolamine condensate of alpha-bromomyristic acid, which is principally a-[N,N-bis (fl-hydroxyethyl) amino] myristic acid diethanolamide, was added to a pickling bath as shown in Example I. After 30 minutes of treatment, a steel coupon was found to have lost 57.8 g./m. No fumes were given off from the bath and the coupon, after rinsing and air-drying was rust-free.

Example VI Pickling baths containing the additives listed below were prepared as shown in Example I. Steel coupons immersed in the various baths did not evidence any sulling after the rinsing and drying steps. Each of the inhibitors effectively controlled metal corrosion and sup pressed the evolution of acid fumes from the bath. The inhibitors, their concentrations, and pickling times were as follows:

Example VII Ten (10) grams of ll-bromoundecylic acid was mixed with twenty (20) grams of dibutylamine and the mixture was refluxed for five hours. The product was not completely soluble in acid, an insoluble oil being present. The soluble portion of the reaction mixture, principally 1l-dibutylaminoundecanoic acid, was an effective corrosion inhibitor and anti-sulling agent for pickling of steel in 20 percent H at C.

Example VIII Twenty (20) grams of alpha-bromomyristic acid was mixed with 35 grams of dibutylamine and the mixture was refluxed for 5 hours. The product was not completely soluble in acid, an insoluble oil being present. The soluble portion of the reaction mixture was an efof the particular material to the water rinse bath. Concentration levels of from .01 percent to about percent by weight of the inhibitor, for example, are satisfactory to prevent rinsed coupons from flash rusting.

The results of the foregoing tests illustrate certain of the outstanding characteristics of the iron and steel treating compositions of the present invention. There is, of course, substantial need in the steel industry for acid corrosion inhibitors which also possess anti-sulling properties. Steel treated with such materials does not require subsequent acid treatment and oiling, and can be electroplated, galvanized, etc., without further processing.

0f almost equal importance to the industry is the fact that the present inhibitors control the escape of harmful acid fumes from the pickling baths. This beneficial property considerably improves working conditions around the bath and prevents acid vapors from corroding surround machinery. The present process and compositions have the further advantage of being fully amenable to established procedures inasmuch as the inhibitor is effective under almost any conditions and does not lengthen pickling time. 1

Of the compositions and methods described in the present invention, those that contain or make use of hydroxyalkylolamino compounds are especially effective. The unexpected success of these materials in particular probably is due at least in part to their unusual solubility characteristics.

An essential feature of the inhibitors of the present compositions is that they have either a primary or a secondary amine group substituted along an alkyl chain of a fatty acid or fatty acid derivative. Such derivatives include fatty esters, fatty amides, and fatty alcohols.

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. An acid bath for pickling ferrous metals containing about 2-25% acid and a minor amount sufficient to inhibit fumes of an inhibitor composition having the general formula: 1

where m is an integer from 0 to 19, n is an integer from 0 to 4, p is an integer from 0 to 19, y is an integer from 0 to 17; and m+2n+ny+3+p=an integer from to 22; where at least one of W and X is selected from the group consisting of [-NRRH]+[AN]-, and -NR'R"; where W is selected from the group consisting of [--NR'RH]+[An]-, and -NRR" when X is selected from the group consisting of H and OH; and where W is selected from the group consisting of [--NR'R"H]+[An]-, NR'R", H and OH when X is selected from the group consisting of and R'R"; and where R is selected from the group consisting of alkyl and alkylol, R" is selected from the group consisting of H, alkyl and alkylol, where Z is selected from the group consisting of CH OH, COOH, CONRR" and COOC H NR'H where s is an integer from 2 to 8 and where [An] is an anion.

2. An acid bath for pickling ferrous metals containing about 225% acid and a small amount suflicient to inhibit acid fumes of 9,10(10,9) diethanolaminohydroxy stearic acid diethanolamide.

3. An acid bath for pickling ferrous metals containing about 225% acid and a small amount sufiicient to inhibit fumes of his [N,N-bis (fi-hydroxyethyl) amino] stearic acid diethanolamide.

4. An acid bath for pickling ferrous metals containing about 2-25% acid and a small amount sufiicient to inhibit fumes of 9,10(l0,9) butyl-ethanolaminohydroxy-stearic acid butylethanolamide.

5. An acid bath for pickling ferrous metals containing about 2-25% acid and a. small amount sufiicient to inhibit fumes of 9,10(10,9)-diisopropanolaminohydroxystearic acid diisopropanolamide.

6. An acid bath for pickling ferrous metals containing about 225% acid and a small amount sufficient to inhibit fumes of a-[N,N-bis(/8-hydroxyethyl)amino] myristic acid diethanolamide.

7. A method of treating ferrous metals which comprises: immersing said metals in an aqueous bath containing a small amount sutficient to inhibit sulling of a composition having the formula:

where m is an integer from 0 to 19, n is an integer from 0 to 4, p is an integer from 0 to 19, y is an integer from 0 to 17; and m+2n+ny+3+p=an integer from 10 to 22; where at least one of W and X is selected from the group consisting of [NRR"H]+[An], and NR'R"; where W is selected from the group consisting of [NR'R"H]+[An]-, and NR'R", when X is selected from the group consisting of H and OH; and where W is selected from the group consisting of [NRR"H] [An]- NR'R", H and OH when X is selected from the group consisting of [--NR'R"H]+[An]- and -NR'R"; and where R is selected from the group consisting of alkyl and alkylol, R is selected from the group consisting of H, alkyl and alkylol, where Z is selected from the group consisting of CH OH, COOH, CONRR" and COOC H NR"H where s is an integer from 2 to 8 and where [An] is an anion.

8. In a process of conditioning ferrous metals wherein said metals are conditioned in an aqueous acid pickling bath the step which comprises immersing said metals in an aqueous bath containing a small amount sufiicient to inhibit sulling of 9,10(10,9) diethanolaminohydroxystearic acid diethanolamide.

9. In a process of conditioning ferrous metals wherein said metals are conditioned in an aqueous acid pickling bath the step which comprises immersing said metals in an aqueous bath containing a small amount suflicient to inhibit sulling of his [N,N-bis(/3-hydroxyethyl) amino] stearic acid diethanolamide.

10. In a process of conditioning ferrous metals wherein said metals are conditioned in an aqueous acid pickling bath the step which comprises immersing said metals in an aqueous bath containing a small amount sufficient to inhibit sulling of 9,10(l0,9) butyl-ethanolaminohydroxystearic acid butyl ethanolamide.

11. In a process of conditioning ferrous metals wherein said metals are conditioned in an aqueous acid pickling bath the step which comprises immersing said metals in an aqueous bath containing a small amount sufficient to inhibit sulling of 9,10(10,9) diisopropanolaminohydroxystearic acid diisopropanolamide.

12. In a process of conditioning ferrous metals wherein said metals are conditioned in an aqueous acid pickling bath the step which comprises immersing said metals in an aqueous bath containing a small amount sufiicient to inhibit sulling of a-[N,N-bis(fl-hydroxyethynamino] myristic acid diethanolamide.

13. The method of claim 7 wherein the aqueous bath is an acid pickling solution.

References Cited in the file of this patent UNITED STATES PATENTS 1,766,902 Harrison June 24, 1930 1,810,946 Calcott et a1 June 23, 1931 (Other references on following page) UNITED STATES PATENTS Macarthur et a1 June 25, 1935 Wilson et a1. May 18, 1937 Guest Mar. 17, 1942 Swern et a1 July 27, 1948 Bried Aug. 21, 1951 Haggard Aug. 21, 1951 Waibel Oct. 12, 1954 Hager et a1. Aug. 6, 1957 10 Gardner et a1 Sept. 24, 1957 Chester et a1 Apr. 22, 1958 Chiddix et a1. Aug. 25, 1959 Gunderson et a1. Sept. 1, 1959 FOREIGN PATENTS France Nov. 10, 1953 Great Britain Sept. 14, 1955 

1. AN ACID BATH FOR PICKLING FERROUS METALS CONTAINING ABOUT 2-25% ACID AND A MINOR AMOUNT SUFFICIENT TO INHIBIT FUMES OF AN INHIBITOR COMPOSITION HAVING THE GENERAL FORMULA:
 7. A METHOD OF TREATING FERROUS METALS WHICH COMPRISES: IMMERSING SAID METALS IN AN AQUEOUS BATH CONTAINING A SMALL AMOUNT SUFFICIENT TO INHIBIT SULLING OF A COMPOSITION HAVING THE FORMULA:
 13. THE METHOD OF CLAIM 7 WHEREIN THE AQUEOUS BATH IS AN ACID PICKLING SOLUTION. 